Development of Building Materials through Alkaline Activation of Construction and Demolition Waste (CDW) - Resistance to Acid Attack

Abstract

Construction and demolition waste (CDW) is a by-product of construction and demolition activity. It consists mostly of inert and non-biodegradable material such as concrete, plaster, metal, wood, plastics etc. CDW is priority waste in the E.U. due to the increased quantities and volumes that are produced. While retrievable items such as brick, wood and metal wires are recycled, concrete, masonry tile and ceramic waste, accounting for more than 60% of CDW, are not being currently recycled. The main objective of this study is to develop a process for obtaining new building materials from CDW using low temperature geopolymerisation in alkaline environment. The two major fractions of the CDW which are not currently being recycled are concrete, mortars, masonry and rubbles for one side and ceramic tile, mosaic and bricks for the other. The major constituents of the first fraction are SiO2 and CaO along with minor concentration of Al2O3 and Fe2O3, mostly crystalline. The major constituents of the latter are SiO2 and Al2O3 and comprise crystalline as well as glassy constituents. The aluminosilicate fraction of both fractions will actively participate in the reaction and for the obtaining of ASH gel (A= Al2O3, S = SiO2, H = H2O), which is the main binding phase. Any deficiency (quantity) in chemical constituents will be compensated by addition of suitable material, e.g., Al2O3 can be compensated with a source of alumina which will be added for alkaline activation reaction. The remaining non aluminosilicate portions such as iron oxide and others will act as filler material. The final product is a very hard ceramic like product. These products can be used for civil engineering applications such as pavement blocks, precast concrete blocks, retaining walls, in general the same use as plain concrete.